1. Field of the Invention
This invention relates to an automatic guided vehicle.
2. Description of the Prior Art
Automatic guided vehicles used for bearing parts or traveling to a desired place to use its robot arm, are known.
The automatic guided vehicle travels on a floor in a works by a driving mechanism along a runway provided on a floor in a works.
FIG. 10 is a bottom view of such a prior art automatic guided vehicle. This automatic guided vehicle has two free casters 3 at the front and rear ends on the centerline of the longitudinal direction of the body 1 and driving wheels 2 at middle portions of both sides of the body 1.
FIG. 11 is a bottom view of another prior art automatic guided vehicle. This automatic guided vehicle has four casters 6 at the four corners of the body 4 and driving wheels 5 at middle portions of the body, directed to one of longitudinal directions of the body 4. In these automatic guided vehicles, a portion of wheels (casters) may be untouched when the surface of the runway is rough.
FIG. 12 is a bottom view of a still another prior art automatic guided vehicle. This automatic guided vehicle has three wheels. A driving wheel 8 is provided at a front end meddle portion and two free casters 9 are provided at rear portion on the both sides. In this type of automatic guided vehicle, when its robot arm is operated such that its center of gravity moves to a corner of the front portion where only one wheel is provided, its body inclines.
To prevent untouchedness of any wheel, an automatic guided vehicle with a suspension mechanism has been provided. Japanese patent provisional publication No. 7-251768 discloses automatic guided vehicles having four wheels and three wheels. In the automatic guided vehicles with four wheels, though running is stable, one or two wheels may be untouched due to roughness of the floor. On the other hand, in the automatic guided vehicles with three wheels, though untouchedness of any wheel is prevented, the position of the automatic guided vehicle becomes unstable when a heavy load is applied to a corner where no wheel is provided. To prevent untouchedness of any wheel, a loading mechanism (spring-loading) is provided to the wheels as a suspension mechanism. The loading mechanism presses a wheel to the floor. However, the position of the body of this automatic guided vehicle may incline when a robot arm is operated, for example.
The aim of the present invention is to provide a superior automatic guided vehicle.
According to the present invention, a first aspect of the present invention is an automatic guided vehicle comprising: a frame having four corners at a bottom portion of said frame; wheels provided to said corners, respectively; a carriage mechanism, including a supporting member provided to said frame to support at least one of said wheels, for changing a vertical position of said at least one of said wheels relative to said frame; a cylinder unit, including: a cylinder tube; a piston movable in the cylinder tube; and covers on both ends of said cylinder tube having ports communicated with the both sides of said piston, respectively, said piston having a rod extending through one of said covers, one of said cylinder tube and said rod being connected to said supporting member of said at least a wheel, the other of said cylinder tube and said rod being connected to said frame; a valve communicated with said ports for allowing said incompressive fluid to enter and exit said cylinder tube through said ports with movement of said piston in an open condition thereof and for inhibiting said incompressive fluid to enter and exit said cylinder tube through said ports in a close condition thereof to lock said vertical position; and control means for controlling said valve in said close condition when said carriage mechanism is stopped.
Preferably, the automatic guided vehicle further comprises a tank communicated with said ports through said valve for reserving said incompressive fluid. Moreover, said tank is arranged above said cylinder unit.
Preferably, said supporting member includes a swing frame provided to said frame under said frame, one of said wheels being provided to said frame, and the remaining three wheels including said at least a wheel are mounted on said swing frame.
According to the present invention, a second aspect of the present invention is an automatic guided vehicle comprising: a frame having four corners at bottom portion of said frame; wheels provided to said corners, respectively; carriage mechanism, including a supporting member provided to said frame to support at least one of said wheels, for changing a vertical position of said at least one of said wheels relative to said frame; driving and steering means for driving and steering at least one of said wheels; driving control means for controlling said driving and steering means; and locking and releasing means for locking and releasing said vertical position in accordance with a request.
Preferably, the automatic guided vehicle further comprises a guide line sensor for detecting a line on a floor, wherein said driving control means control said driving and steering means in accordance with said guide line sensor.
Preferably, said locking and releasing means comprises: a cylinder unit including: a cylinder tube; a piston movable in the cylinder tube; and covers on both ends of said cylinder tube having ports communicated with the both sides of said piston, respectively; said piston having a rod extending through one of said covers, one of said cylinder tube and said rod being connected to said supporting member of said at least a wheel, the other of said cylinder tube and said rod being connected to said frame; a valve communicated with said ports for allowing said incompressive fluid to enter and exit said cylinder tube through said ports with movement of said piston in an open condition thereof and for inhibiting said incompressive fluid to enter and exit said cylinder tube through said ports in a close condition thereof to lock said vertical position.
Preferably, the automatic guided vehicle further comprises a tank, arranged above said cylinder unit, communicated with said ports through said valve for reserving said incompressive fluid.
Preferably, said supporting member includes a swing frame provided under said frame to change said vertical position, one of said wheels is provided to said frame, and the remaining three wheels including said at least a wheel are mounted on said swing frame.